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  • 1
    Online Resource
    Online Resource
    Video_1.mp4
    Frontiers Media SA ; 2022
    In:  Frontiers in Marine Science Vol. 9 ( 2022-5-12)
    Details
    In: Frontiers in Marine Science, Frontiers Media SA, Vol. 9 ( 2022-5-12)
    Abstract: A deep-water acoustic observatory for real-time detection and localization of vocalizing sperm whales was developed, deployed and operated for two 3-month periods in summer 2020 and 2021, off south-west Crete in the Eastern Mediterranean Sea, in the framework of the SAvEWhales project. Regular clicks, pulsed sounds produced by the diving animals, were detected and localized using a large-aperture array of three hydrophones suspended from surface buoys at depths of about 100 m and 1-2 km apart. Travel times of significant arrivals, arrivals with magnitude above a certain threshold, were extracted in situ and transmitted, together with other supporting data, via mobile broadband to a land-based analysis center. Upon reception, the data from all buoys were combined to enable detection and 3D localization of vocalizing animals exploiting direct and surface-reflected arrivals and using a Bayesian approach. The large separations between hydrophones resulted in small localization uncertainties for ranges up to 7 km; on the other hand, they posed significant challenges related to synchronization and peak association between the buoys, as well as because of the directionality of sperm whale clicks. The integrated observing system which has been successfully tested in detecting and localizing sperm whales can have a significant effect in mitigating ship strikes on whales, the prominent threat for sperm whales in the Eastern Mediterranean Sea, by providing information about the presence and location of the animals in real time. The design and implementation, as well as results from the operation and validation of the acoustic observatory are presented.
    Type of Medium: Online Resource
    ISSN: 2296-7745
    URL: Article
    URL: Article
    DOI: 10.3389/fmars.2022.873888
    DOI: 10.3389/fmars.2022.873888.s001
    Language: Unknown
    Publisher: Frontiers Media SA
    Publication Date: 2022
    detail.hit.zdb_id: 2757748-X
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  • 2
    Online Resource
    Online Resource
    Correction: Skarsoulis et al. Prediction of Shipping Noise in Range-Dependent Environments. J. Mar. Sci. Eng. 2023, 11, 290
    MDPI AG ; 2023
    In:  Journal of Marine Science and Engineering Vol. 11, No. 7 ( 2023-07-24), p. 1472-
    Details
    In: Journal of Marine Science and Engineering, MDPI AG, Vol. 11, No. 7 ( 2023-07-24), p. 1472-
    Abstract: There was an error in the original publication [...]
    Type of Medium: Online Resource
    ISSN: 2077-1312
    URL: Article
    DOI: 10.3390/jmse11071472
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2738390-8
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  • 3
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    Online Resource
    Sensitivity kernels of finite-frequency travel times in ocean acoustic tomography
    Acoustical Society of America (ASA) ; 2004
    In:  The Journal of the Acoustical Society of America Vol. 115, No. 5_Supplement ( 2004-05-01), p. 2617-2617
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 115, No. 5_Supplement ( 2004-05-01), p. 2617-2617
    Abstract: Wave theoretic modeling is applied to obtain travel-time sensitivity kernels representing the amount by which travel times are affected by localized sound-speed variations anywhere in the medium. In the ray approximation travel times are sensitive to medium changes only along the corresponding eigenrays. In the wave-theoretic approach the perturbations of peak arrival times are expressed in terms of pressure perturbations, which are further related with the underlying sound-speed perturbations using the first Born approximation. In this way, an integral representation of travel-time perturbations is obtained in terms of sound-speed perturbations; the associated kernel represents the spatial sensitivity of travel times to sound-speed perturbations. The application of the travel-time sensitivity kernel to an ocean acoustic waveguide gives a picture close to the ray-theoretic one in the high-frequency case but significantly differs at lower frequencies. Low-frequency travel times are sensitive to sound-speed changes in areas surrounding the eigenrays, but not on the eigenrays themselves, where the sensitivity is zero. Further, there are areas of positive sensitivity, where, e.g., a sound-speed increase results in a counter-intuitive increase of arrival times. These findings are confirmed by independent forward calculations.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4784805
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2004
    detail.hit.zdb_id: 1461063-2
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  • 4
    Online Resource
    Online Resource
    Structure and stability of wave-theoretic kernels in the ocean
    Acoustical Society of America (ASA) ; 2013
    In:  The Journal of the Acoustical Society of America Vol. 134, No. 4 ( 2013-10-01), p. 3318-3331
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 134, No. 4 ( 2013-10-01), p. 3318-3331
    Abstract: Wave-theoretic modeling can be applied to obtain travel-time sensitivity kernels (TSKs) representing the amount ray travel times are affected by sound-speed variations anywhere in the medium. This work explores the spatial frequency content of the TSK compared to expected ocean variability. It also examines the stability of the TSK in environments that produce strong sensitivity of ray paths to initial conditions. The conclusion is that the linear TSK model is an effective predictor of travel-time changes and that the rays perform nearly as well as the full-wave kernel. The TSK is examined in physical space and in wavenumber space, and it is found that this is the key to understanding how the travel time reacts to ocean perturbations. There are minimum vertical and horizontal length scales of ocean perturbations that are required for the travel time to be affected. The result is that the correspondence between true travel times and those calculated from the kernel is high for large-scale perturbations and somewhat less for the small scales. This demonstrates the validity of ray-based inversion of travel time observations for the cases under study.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4818846
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2013
    detail.hit.zdb_id: 1461063-2
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  • 5
    Online Resource
    Online Resource
    Peak-time sensitivity kernels for noise cross-correlation envelopes
    Acoustical Society of America (ASA) ; 2022
    In:  The Journal of the Acoustical Society of America Vol. 151, No. 4 ( 2022-04-01), p. 2353-2366
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 151, No. 4 ( 2022-04-01), p. 2353-2366
    Abstract: The envelope of the time-lagged cross-correlation of an underwater noise field between two hydrophones can under certain conditions be used as a proxy for active acoustic receptions between the two locations enabling the study of ocean variability. Previous work looked at the sensitivity of cross-correlation peak amplitudes with respect to the distribution of the noise sources. The present study examines the sensitivity of the cross-correlation envelope peak times with respect to changes in the sound-speed distribution. A wave-theoretic scheme allowing for finite-frequency calculations in two and three dimensions, combined with the Born approximation for perturbations of the Green's function and the peak arrival approach, is used to obtain sensitivity kernels with respect to environmental (sound-speed) changes. These kernels provide a way to infer ocean structure from the cross-correlation peaks, considered as observables on their own and valid even in cases where the cross-correlation function does not approximate the time-domain Green's function between the two receivers. The sensitivity behavior is studied for different propagation conditions and noise-source distributions, ranging from spatially distributed uncorrelated noise sources to point sources, such as individual ships. Deviations from linearity are addressed and discussed.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/10.0010044
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2022
    detail.hit.zdb_id: 1461063-2
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  • 6
    Online Resource
    Online Resource
    Enhanced Pulsed-Source Localization with 3 Hydrophones: Uncertainty Estimates
    MDPI AG ; 2021
    In:  Remote Sensing Vol. 13, No. 9 ( 2021-05-07), p. 1817-
    Details
    In: Remote Sensing, MDPI AG, Vol. 13, No. 9 ( 2021-05-07), p. 1817-
    Abstract: The uncertainty behavior of an enhanced three-dimensional (3D) localization scheme for pulsed sources based on relative travel times at a large-aperture three-hydrophone array is studied. The localization scheme is an extension of a two-hydrophone localization approach based on time differences between direct and surface-reflected arrivals, an approach with significant advantages, but also drawbacks, such as left-right ambiguity, high range/depth uncertainties for broadside sources, and high bearing uncertainties for endfire sources. These drawbacks can be removed by adding a third hydrophone. The 3D localization problem is separated into two, a range/depth estimation problem, for which only the hydrophone depths are needed, and a bearing estimation problem, if the hydrophone geometry in the horizontal is known as well. The refraction of acoustic paths is taken into account using ray theory. The condition for existence of surface-reflected arrivals can be relaxed by considering arrivals with an upper turning point, allowing for localization at longer ranges. A Bayesian framework is adopted, allowing for the estimation of localization uncertainties. Uncertainty estimates are obtained through analytic predictions and simulations and they are compared against two-hydrophone localization uncertainties as well as against two-dimensional localization that is based on direct arrivals.
    Type of Medium: Online Resource
    ISSN: 2072-4292
    URL: Article
    DOI: 10.3390/rs13091817
    Language: English
    Publisher: MDPI AG
    Publication Date: 2021
    detail.hit.zdb_id: 2513863-7
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  • 7
    Online Resource
    Online Resource
    Time series of temperature in Fram Strait determined from the 2008–2009 DAMOCLES acoustic tomography measurements and an ocean model
    American Geophysical Union (AGU) ; 2016
    In:  Journal of Geophysical Research: Oceans Vol. 121, No. 7 ( 2016-07), p. 4601-4617
    Details
    In: Journal of Geophysical Research: Oceans, American Geophysical Union (AGU), Vol. 121, No. 7 ( 2016-07), p. 4601-4617
    Abstract: Tomography accurately measures path‐averaged temperature in Fram Strait An ocean model misrepresents both mean and variability compared to data Tomographic data can be used to correct ocean models through data assimilation
    Type of Medium: Online Resource
    ISSN: 2169-9275 , 2169-9291
    URL: Issue
    URL: Article
    DOI: 10.1002/jgrc.v121.7
    DOI: 10.1002/2015JC011591
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2016
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 161667-5
    detail.hit.zdb_id: 3094219-6
    SSG: 16,13
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  • 8
    Online Resource
    Online Resource
    Clicks from Cuvier’s beaked whales, Ziphius cavirostris (L)
    Acoustical Society of America (ASA) ; 2002
    In:  The Journal of the Acoustical Society of America Vol. 112, No. 1 ( 2002-07-01), p. 34-37
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 112, No. 1 ( 2002-07-01), p. 34-37
    Abstract: Recordings of pulsed sounds (clicks) from Cuvier’s beaked whales are presented. Such recordings have not been reported in the literature before. Spectrogram analysis of data collected off SW Crete (Greece) from 1998 to 2000 revealed numerous sequences of clicks. Click pulses had durations of about 1 ms and their energy content in the audible spectrum presented a narrow peak between 13 and 17 kHz. Sequences of 35–105 clicks, with duration 15–44 s, were separated by short intersequence pauses of 3–10 s. Interclick intervals appeared fairly constant, primarily oscillating between 0.40 and 0.50 s. Characteristics of Cuvier’s beaked whale clicks were consistent with echolocating cetaceans, suggesting that this species do echolocate.
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.1479149
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2002
    detail.hit.zdb_id: 1461063-2
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  • 9
    Online Resource
    Online Resource
    Sensitivity kernels for finite-frequency ocean acoustic observables
    Acoustical Society of America (ASA) ; 2004
    In:  The Journal of the Acoustical Society of America Vol. 116, No. 4_Supplement ( 2004-10-01), p. 2634-2634
    Details
    In: The Journal of the Acoustical Society of America, Acoustical Society of America (ASA), Vol. 116, No. 4_Supplement ( 2004-10-01), p. 2634-2634
    Abstract: Wave theoretic modeling was applied to obtain sensitivity kernels representing the amount by which ocean acoustic observables, such as pressure, intensity, or arrival times, are affected by localized sound-speed variations anywhere in the medium. These kernels can be derived using the first Born approximation, yielding an integral representation of observable perturbations as functionals of sound-speed perturbations. The kernel in each integral represents the spatial sensitivity of the observable to sound-speed perturbations in the medium. The travel-time sensitivity kernel represents a full-wave generalization of the highly localized ray kernel from geometric optics. This work extended recent wave-theoretic results for the travel-time sensitivity kernel for short-range propagation in simple environments to long-range transmissions in more complicated ocean environments relevant to ongoing propagation and inversion experiments. It was shown that the geometry of the wave-theoretic sensitivity kernels is related to the geometry of Fresnel volumes surrounding eigenrays, provided that the effects of refraction are taken into account for the calculation of the latter. [Work supported by ONR.]
    Type of Medium: Online Resource
    ISSN: 0001-4966 , 1520-8524
    URL: Article
    DOI: 10.1121/1.4785508
    RVK:
    EQ 1000
    Language: English
    Publisher: Acoustical Society of America (ASA)
    Publication Date: 2004
    detail.hit.zdb_id: 1461063-2
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  • 10
    Online Resource
    Online Resource
    Prediction of Shipping Noise in Range-Dependent Environments
    MDPI AG ; 2023
    In:  Journal of Marine Science and Engineering Vol. 11, No. 2 ( 2023-01-30), p. 290-
    Details
    In: Journal of Marine Science and Engineering, MDPI AG, Vol. 11, No. 2 ( 2023-01-30), p. 290-
    Abstract: A prediction model for shipping noise in range-dependent environments based on coupled-mode theory is presented, as an enhancement to existing adiabatic normal-mode approaches without a significant increase in computational effort. Emphasis is placed on the categorization of environmental changes and precalculation and storage of eigenvalues, eigenfunctions and coupling matrices, such that they can be looked up and restored to efficiently compute the acoustic field of arbitrary noise source distributions over a given sea area. Taking into account that the water depth is the primary factor determining the number of propagating modes for a particular frequency, coupling is applied only in the case of changing bathymetry, whereas changes in the water sound-speed profile and/or the geoacoustic characteristics are treated adiabatically. Examples of noise calculations are given for benchmark setups in the Eastern Mediterranean Sea and comparisons with fully adiabatic predictions are drawn. Moreover, the effect of applying range propagation limitations in a numerical propagation model for shipping noise predictions is demonstrated.
    Type of Medium: Online Resource
    ISSN: 2077-1312
    URL: Article
    DOI: 10.3390/jmse11020290
    Language: English
    Publisher: MDPI AG
    Publication Date: 2023
    detail.hit.zdb_id: 2738390-8
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